This proposal requests funding to substantially upgrade the variable frequency pulsed EPR Facility in the Department of Chemistry at the University of Arizona by acquiring a high field (1.99 Tesla) magnet system, including power supply, liquid helium cryostat with accessories and temperature controller, and a timing/ data acquistion module. Presently, a single 1.4 Tesla magnet system that is an integral part of the Bruker ESP300E X-band CW EPR spectrometer must also serve the requirements for the three unique broadband-pulsed EPR spectrometers that operate over the 2-8, 8-18 and 26-40 GHz ranges. This arrangement greatly limits the research output of the EPR Facility because only one type of EPR experiment can be running at any one time. In addition, the frequent changing among the spectrometers for the single available magnet system usurps valuable instrument time that could be used for productive research. Moreover, the 1.4 Tesla field of the existing magnet is too low to enable EPR signals with g < 2.0 to be studied by high resolution pulsed EPR techniques near 40 GHz. This high frequency range is essential for pulsed EPR studies of several of the biomolecules of the investigators of this proposal, including investigation of 14N, 15N interactions in heme proteins and Rieske proteins and 17-O in molybdenum enzymes, all of which have g-values spread below g=2. The requested 1.99 Tesla magnet system with power supply, liquid helium cryostat with accessories and temperature controller, and a timing/data acquisition module, will handle the ever increasing demands for experiments on metallobiomolecules using the existing 8-18 and 26-40 GHz pulsed broadband EPR spectrometers as well as provide increased access of users to the CW X-band and pulsed S/C band (2-8 GHz) spectrometers.